Just read the article, "The Web of Life: Plant Biodiversity" in Acres, Vol 40, no 5. Here are some quotes and facts:
"We've viewed our livestock and ourselves as isolated organisms, rather than recognizing that we are all "super organisms," or more accurately, complex ecosystems that are self-organizing, cooperating, self-sacrificing and constantly communicating with each other."
Plants synthesize plant secondary metabolites (PSM), which "protect themselves from weather, UV radiation, insects, diseases, and excessive grazing. These PSMs become a major component in the healthy metabolism and imunity of animals and humans that consume them."
"So far, science has isolated over 80,000 of these compounds." Some are: lutein (kale and egg yolk), lycopene (tomato), and EGCG (green tea). All green plants produce PSMs.
"When livestock consume dozens of species of plants, there is a synergism involved that allows animals to increase the efficiency of digestion as well as the elimination of toxins, both those inherent in the feeds (all plants contain both nutrients and toxins) and those by-products of metabolism."
70-80% of the immune system is seated in the gut, so this "helps animals ward off pathogens and parasites before they become opportunistic."
Multi-species grazers offer: "more kinds of manure/microbes, gut microbes, different kinds of parasites that can't colonize every host, thus interrupting the parasite's cycle." And encourage wildlife.
One thing leads to another, and before you know it, you have set up a farm ecosystem that takes care of itself!